This invention concerns thermoforming apparatus in which multiple products are formed from preheated sheet plastic material by drawing the sheet material into conformity with mold cavities using vacuum and/or air pressure to form a plurality of products. For such products, as disposable plastic drinking cups, a number of products are formed simultaneously usually in a rectangular array of several rows, such as an 8xc3x9710 array.
In such apparatus, plug assists are usually used for products such as large disposable cups to aid the stretching of the sheet material as it is drawn into a female mold cavity to control the stretching of the plastic occurring when the heated sheet material is drawn into the cavity. The plug assists are male shaped tooling members fixed to a plate in rows, each plug assist aligned with a respective female cavity and extending towards the same in the thermoforming machine. The distending of the plastic sheet material by the plug assists as well as the clamping of the material prevents excessive localized thinning of the material as it is stretched into conformity with the mold cavity by the action of the vacuum and/or air pressure.
Sometimes, various sized parts are run on the same thermoforming machine, necessitating changing the tooling, including the plug assists. Also, individual broken plug assists occasionally have to be replaced.
In such situations, the plug assists are manually disassembled using suitable tools
In the past, arrangements have been incorporated in the plug assist mountings to speed the process of accomplishing changeover, since as many as 80 or more such plug assist removals and replacements could be required to be carried out.
In one arrangement, a series of lengthwise cam bars extending along rows of plug assists are operated to release all of the plug assists in each row from their respective bases, (or to lock all of the same thereto), but these arrangements have required costly precision machined components.
Another approach has been to install pneumatic or electro-mechanically operated mountings which can be simultaneously released. This approach is also quite costly.
Any connection for the plug assists must be secure and not be loosened over the course of thousands of press cycles since loosening could cause severe tooling damage. Furthermore, the mounting must provide precision location of the plug assists in order to be accurately aligned with the respective mold cavity to create proper stretching of the plastic sheet material.
It is the object of the present invention to provide a simplified, less costly plug assist mounting for thermoformer tooling which accurately locates the plug assist while still allowing a quick changeover and insuring a very secure connection.
This object and others which will become apparent upon a reading of the following specification and claims are achieved by providing a precision quick change mounting for each individual plug assist which allows a rapid manual installation for each individual plug assist without the use of tools, which can be accomplished with little more time and effort than is required to simply lift each plug assist from the base plate. Thus, the time for making a changeover is approximately the same as for simply lifting each plug assist from the base plate as was required in the prior designs using a cam bar release or pneumatic or electro-mechanical simultaneous release for multiple plug assists, but at a much lower cost and with improved reliability.
The mounting according to the invention comprises a boss projecting up from an anchor piece attached to the base plate, or alternatively, attached to the plug assist driving rods, to hold the array of plug assists. A cross dowel pin has ends projecting out radially from opposite sides of the boss at an intermediate height thereof.
The plug assist itself, which may be formed of syntactic foam, is attached as by gluing to a plug bottom piece, which is in turn secured such as by threads or other method to the plug base. The plug base is formed with an internal bore sized to slidably receive the anchor boss to be accurately radially located thereon engaging a radial face of the flange of the anchor piece to be accurately located vertically on the anchor piece.
Vertically extending radial slots are machined into the plug base piece located to receive the dowel cross pin ends when the plug base piece is received over the boss in a correct angular orientation. The vertical slots each extend to respective horizontal slot extending circumferentially along the perimeter of a base piece side wall, allowing the base piece to be manually rotated to cause the pin ends to travel to the end of a respective horizontal slot.
Each of a pair of opposing spring plungers are located adjacent the end of a respective horizontal slots so as to yieldably engage the sides of the pin end at points past the center thereof to capture the same and provide a detent.
The bottom of the horizontal slots accurately locates the base piece vertically on the base.
Alternatively, the cross pin can be yieldably mounted on the boss and a cam ramp ascended by the pin ends (cam rollers may be mounted on the pin ends to reduce friction) until a radiused seat is reached providing a detent.
That is, the boss and its pin can be mounted to the plug base. The receive, in turn, is then mounted to the plug base plate, or to the plug driving rods.
This low cost mechanical mounting accurately and securely locates each individual plug assist on the base plate allowing them to be quickly and easily removable almost as quickly and easily as simply lifting the plug assists after activation of cam bars, or pneumatic or electromechanically operated mounts.